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Lamina I neurons sending their axons into the spinothalamic tract are thought to play a crucial role in nociception, but many spinothalamic fibers do not originate from lamina I neurons. In cat, no consensus exists about what percentage of the spinothatamic tract cells are located in lamina I. After wheat germ agglutinin-conjugated horseradish peroxidase injections that covered large parts of the thalamus, retrogradely labeled cells were plotted and counted in all segments of the spinal cord. Results show that, averaged over all spinal segments, the percentage of labeled lamina I neurons was 4.9-14.2%. These results demonstrate that, in contrast to what is concluded in several previous studies, lamina I in the cat provides only a limited part of the total spinal input to the thalamus. (C) 2004 Elsevier Ireland Ltd. All rights reserved.

The number and distribution of lamina I neurons projecting to the periaqueductal gray (PAG) were examined by a retrograde tracing study in the cat. WGA-HRP injections in the intermediate and caudal FAG resulted in as much as 1600 labeled lamina I neurons throughout the length of the spinal cord, counted in a 1:4 series of sections. The lamina I-PAG projection was predominantly contralateral and most labeled lamina I neurons were found in the enlargements. Comparing these results with the number of lamina I-thalamic neurons leads to the conclusion that in the cat about three times as many lamina I neurons project to the FAG than to the thalamus. Considering this, one can conclude that the spino-PAG system is a virtually neglected area in pain research. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.

The spinal cord location of the motoneurons innervating the psoas and iliacus muscles was determined in the golden hamster. The results of single and double labeling studies, using the retrograde tracers horseradish peroxidase (HRP) and cholera toxin B-subunit (CTB), showed that both psoas and iliacus motoneurons were present ventrolaterally in the ventral horn in the caudal L1 to rostral L5 lumbar spinal segments with their motoneurons intermingled in one cell group. Further retrograde tracing studies demonstrated abdominal muscle motoneurons ventrolaterally in the ventral horn of the LI and upper L2 segments. Double labeling experiments revealed that at these levels (caudal L1 and rostral L2), the abdominal muscle motoneurons were located dorsomedial to the psoas and iliacus motoneurons. (C) 1997 Elsevier Science Ireland Ltd.

Stimulation of the pontine micturition center (PMC) results in micturition, i.e. an immediate relaxation of the urethral sphincter and a contraction of the detrusor muscle of the bladder. The PMC generates the bladder contraction by way of a direct excitatory pathway to the parasympathetic bladder motoneurons in the sacral cord. The idea is that the PMC produces the relaxation of the urethral sphincter via direct projections to GABAergic neurons in the dorsal gray commissure (DGC), which, in turn, inhibit the urethral sphincter motoneurons. According to this hypothesis, electrical stimulation in the DGC in three cats should result in relaxation of the urethral sphincter. The results were in total agreement with this concept. During DGC stimulation a sharp decrease of the urethral pressure was found, the strength of which depended completely on the amplitude of the electrical stimulation. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.

In 11 cases [3H]leucine injections were made in various parts of the red nucleus (NR) and surrounding area. The autoradiographical tracing results confirmed the existence of a somatotopic organization in the location of the rubrospinal neurons. Moreover the results demonstrated direct NR projections to the most dorsolaterally located motoneuronal cell group in the C8 and upper T1 spinal segments and some ipsilaterally descending rubrospinal fibers terminating in the lateral part of the cervical intermediate zone.